Ceiling height increase adds value? Until when is it possible to change the height?

I think it also depends on the room size. A small room with a high ceiling probably feels less cozy. Conversely, the lower ceiling in a large room probably feels more oppressive than in a small one. However, I don't believe that 10cm more or less in room height have any impact on the value of the house.

Good that you know about it and I don't, even though I accompany a few hundred apartments in construction projects every year...
However, I made a typo regarding the door height. 210 is correct (or exactly 211/209.75 as higher options or 198.5/197.2). With a ceiling height of 270cm, my clients start, of course depending on the floor structure. I myself last built 267 for myself.

OK then we're talking past each other! I of course assumed the finished dimension, 2.70 as raw construction measurement is quite common. My experience with the finished dimension:

2.50 standard in general contractor / developer houses and still very often installed
2.60 mostly people who have given it some thought and build themselves
2.70 or more only certain types of houses or enthusiasts...

My experience with the finished measurement:

What do you think about the resale value? And can you see the difference between 2.5m and 2.6m?

Resale value is not that important when you build a house for yourself. Generally, (I think) more people like higher ceilings. But most have standard (2.40 prefab height). You probably won’t get back the money for higher ceilings (more enclosed space, more expensive shell, larger windows, more expensive maintenance for heating and ventilation...). Location and so on play a much more important role. In Munich, you can sell a dilapidated shack on a small plot for millions, while in the middle of nowhere you might have to give away a castle with a park with a theoretical million value soon. You want to build a house that will still be within the standard range. Go into a few houses and “feel” it. Then measure the ceiling height... With 2.5 or 2.55 you are high enough.

So I would first take a look at the development plan. What does it say? Is there anything about the eaves or ridge height? If yes, then you must strictly adhere to it. The architect designs the house taking the development plan into account. The building permit is granted based on these plans. If the final survey later shows that your eaves/ridge height is higher than allowed, a demolition or reduction might be required.

Absolutely no relevance to the resale value. If anything, it reduces the potential buyer pool, but you only need more than 1 buyer.